This invention relates to a display system which can be used, for example, inside a vehicle such as a tank in order to monitor at least part of the surrounding field of view.
In modern display systems the display generator is typically a cathode ray tube (CRT) which is designed to present minimal distortion to a viewer of the display. However, in some instances, the display generator forms part of a larger display system which utilises an optical system to view the generated display, typically under magnification. In such circumstances, there is a problem in that even a well designed optical system introduces distortion not originally present in the CRT. This is particularly true of biocular magnifiers (corresponding to U.S. Pat. No. 4,183,624), such as those exemplified in UK patent specification No. 1537276. A typical biocular magnifier introduces distortion which increases towards the edge of the CRT such that an observer, instead of seeing a perfectly rectangular view, instead perceives a view having "pin cushion" distortion, or in some cases, "barrel" distortion.
Such distortion can be overcome to some extent by designing into the optical system compensating elements but this usually increases the cost and complexity of the system as a whole and is not alway satisfactory, particularly where there are constraints on the size of the system, e.g. when installed within a military vehicle such as a tank. An example of this type of correction is shown in UK patent application No. 2159295A (corresponding to U.S. application Ser. No. 4,537,483), in which barrel distortion introduced by a biocular magnifier in a microscope viewing system is corrected by means of an optical element shaped to provide optical distortion in an opposite sense to that of the biocular such that an observer is able to view a substantially undistorted image.
It is an object of the first aspect of the invention to provide a display system in which the need for optical correction of distortion, as defined above, is obviated.